frame



Concept

Thephysicalmemoryisdividedintofixed-sizeblockscalledframes.Incontrast,logicalmemoryisdividedintoblocksofthesamesize,calledpages.

Networktransmission

Framesareformedbyspecificsoftwarecallednetworkdrivers,andthensenttothenetworkcablethroughthenetworkcard,andreachtheirdestinationmachinethroughthenetworkcable.Theoppositeprocessisperformedononeend.TheEthernetcardofthereceivingmachinecapturestheseframes,tellstheoperatingsystemthattheframeshavearrived,andthenstoresthem.Itisinthistransmissionandreceptionprocessthatthesnifferwillbringsecurityproblems.

"Frame"dataconsistsoftwoparts:frameheaderandframedata.Theframeheaderincludesthelocationofthereceiver'shostphysicaladdressandothernetworkinformation.Theframedataareacontainsadatabody.Toensurethatthecomputercaninterpretthedatainthedataframe,thetwocomputersuseacommoncommunicationprotocol.ThecommunicationprotocolusedbytheInternetisreferredtoasIP,orInternetProtocol.TheIPdatabodyiscomposedoftwoparts:thedatabodyheaderandthedataareaof​​thedatabody.ThedatabodyheaderincludesIPsourceaddressandIPdestinationaddress,andotherinformation.Thedataareaof​​thedatabodyincludesUserDataProtocol(UDP),TransmissionControlProtocol(TCP),andotherinformationaboutthedatapacket.Thesedatapacketsallcontainadditionalprocessinformationandactualdata.

TheminimumframelengthofEthernet

OnceaCSMA/CDconflictoccurs,itmustbedetectedbyeverynode.Ethernethasspecifiedtheminimumtransmissiongapandminimumframelengthtoavoidconflictsasmuchaspossible.Ifthedistancebetweenthetwonodesisverylongandtheframeissmall,thereceiverstartstosendtheframebeforetheframereachesthedestination.Inthisway,thereceiver'sframehasbeensentandthedataisstillbeingtransmittedinthechannel,andithasnotyetreachedthedestinationnode.Sincethereceivingnodehasnotreceivedtheinformation,itmistakenlybelievesthatthechannelisidle,andmaytransmitdataoutwards,whichwillcausenewchannelconflicts.Inthesendingsection,itwasmistakenthatthesendingwassuccessful.Signaltransmissionistime-delayed,soittakesacertainamountoftimetodetectcollisions,whichdeterminesthattheEthernetmusthaveaminimumframelengthlimit.

ThemaximumframelengthofEthernet

MTUreferstothemaximumdatapacketsizethatcanbepassedonthecommunicationprotocol,usuallyrelatedtothecommunicationinterface.

Datacommunicationinthenetworkdividesthedataintomultiplesegmentssuitablefortransmissioninthenetwork.Thesedataaresmallenoughtoensurethatthelargestdatacanalsopassthroughthesmallestforwardinglinkinthenetwork.Thefragmentationprocessoccursinthe3rdand4thlayersoftheOSImodel.The4thlayeristhemostimportantlayerintheOSImodel.Itmainlycontrolsthetransmissionbasedonthewindow,nottheMTU.

Duringthedatatransmissionprocess,thesenderandreceiveraresentfastorslowthroughthetrialofQOS.Intheprocessofnetworktransmission,iftoolargedataisfound,thelargerdatapacketwillbeforcedtogroup.InEthernet,thelargestprotocoldataunitis1500bytes.Ofcourse,thisdatadoesnotincludetheframeheaderpartofthedata.Inthegroupingprocess,eachfragmenthasasequencenumber,thepurposeisthatafterthereceiverreceivesthedata,itcanbereorganizedcorrectly.Thelargesttransmissionunitinthenetworkistoensurethatalldatacanpassthroughalllinknodesduringnetworklinktransmission.

Becausethechannelissharedbyallnodes,thedataframeistoolong,eachframewilltakealongtimeduringthedatatransmissionprocess,andsomenodeswillwaittoolong;thedataarrivesatthereceiverAfterthepoint,thesizeofthereorganizationbufferofthetargetnodeislimited,andsomesentdatamayexceedthebuffersizeofthereceivingendbyalot,causingbufferoverflow.Inordertopreventnodesfromoccupyingtoolong,aruleof1,500byteshasbeenformulatedinthenetworktoensurethefairnessofchannelownership.

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